250 REPORTS ON INVi;STlGATlONS AND PROJECTS. 



as far as it is possible at the present time to decide, are never predetermined, 

 but are always the direct result of the response of the developing organism 

 to stimuli, and these stimuli seem to be primarily external. Although it is 

 becoming clearer with each year's work that variations are responses to 

 stimuli, as yet there are no indications that the variations are trophic in 

 their nature, but that different stimuli produce the same results. 



A point of importance is the continuity of variations found, there being 

 no indications that there exists in any sense the isolation of variations or 

 " unit characters " as postulated by De Vries. Variations may form with 

 rapidity, but there are always to be distinguished intermediate steps which 

 grade into one another. 



The data and conclusions concerning heredity derived from these investi- 

 gations, while of interest and suggestive, may easily be overestimated in their 

 value. In Chrysomelid beetles not all inheritance is Mendelian in character; 

 but as far as determined only characters that are " general characters" in 

 the organism are thus inherited. The minor characters differ in different 

 species and also according to the character, no general rule being followed 

 as far as it has been possible to discover. It is hoped that the pedigree 

 cultures now going can be continued without accident for a term of years, 

 thus giving data upon the questions of heredity from known pedigreed 

 families. 



Whether species have developed by accumulated variations and natural 

 selection or by mutation and natural selection is perhaps the question of 

 greatest interest at this time. The results derived from the study of varia- 

 tion and the data of the transplantation experiments, when added to the 

 information gained in nature of this problem, shows that in these beetles the 

 method of evolution is an orthogenetic, rapid transmutation in response to 

 stimuli, according to the method of trial and error, with natural selection 

 and segregation acting as the factors to conserve the developing race. All 

 evidence points to the general conclusion that species have arisen through 

 the progressive and continuous modal shifting of the evolving, segregated 

 group, the mode representing the optimum or most stable condition existing 

 between the organism and its environment. " Mutations " — that is, large or 

 extreme variations — do not seem to play any part in the process as carried 

 on in nature, but are exterminated, in the instances observed, as soon as 

 they arise. 



"Wilson, Edmund B,, Columbia University, New York, N. Y. Grant No. 370. 



Researches in the chromosomes of insects and other animals with reference to 



the cytological basis of sex-prodiiction and Mendelian inheritance. $500. 



Professor Wilson made an extensive field trip during the summer, south 



as far as Georgia and then westward across the continent in the southern 



region. A very large amount of material was secured, which will require a 



long time to work up in full. 



